Nice! That version runs in 6 milliseconds on my machine, fastest of
all the code posted so far. One more idea: use 'unchecked-inc'
instead of 'unchecked-add'. This takes it under 3 milliseconds in my
tests.
(defn java-like [^bytes cpu_array]
(let [buffer-size (int buffer-size)]
(loop [i (int 0)]
(if (< i buffer-size)
(let [i2 (unchecked-inc i)
i3 (unchecked-inc i2)
i4 (unchecked-inc i3)
a (aget cpu_array i4)]
(amove cpu_array i3 i4)
(amove cpu_array i2 i3)
(amove cpu_array i i2)
(aset cpu_array i a)
(recur (unchecked-inc i4)))))))
On Jan 30, 8:15 am, Bill James <w_a_x_...@yahoo.com> wrote:
> GrumpyLittleTed wrote:
> > Part of the difference (under 1.2) is due to the (substantial)
> > overhead of accessing the buffer-size var on every iteration.
>
> > I ran a quick check and using David's version of the code result
> > averaged 17.2ms. Just changing buffer-size to a local with using (let
> > [buffer-size (int 1920000)]...) the time dropped to an average 3.4ms.
>
> Great! Now I remember that that same technique is used in Lua.
> See long this version takes.
>
> (set! *warn-on-reflection* true)
>
> (def buffer-size 1920000)
> (def array (byte-array buffer-size))
>
> (defmacro add [m n] `(unchecked-add (int ~m) (int ~n)))
> (defmacro amove[a i j] `(aset ~a ~j (aget ~a ~i)))
>
> (defn java-like [^bytes cpu_array]
> (let [buffer-size (int buffer-size)]
> (loop [i (int 0)]
> (if (< i buffer-size)
> (let [ i2 (add i 1)
> i3 (add i 2)
> i4 (add i 3)
> a (aget cpu_array i4)
> ]
> (amove cpu_array i3 i4)
> (amove cpu_array i2 i3)
> (amove cpu_array i i2)
> (aset cpu_array i a)
> (recur (add i 4)))))))
>
> (dotimes [_ 10]
> (time
> (dotimes [_ 1]
> (java-like array))))
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